Due to their relatively high thermal conductivities, composite metal powders which contain refractory metals (e.g., W or Mo) in combination with high conductivity metals (e.g., Cu or Ag) are used in many diverse applications., such as, as heat sinks and electrical contacts for the electronics industry. Such composites have been made by a number of methods. For example in one method, known as infiltration, a shaped article formed from a sintered mass of tungsten or molybdenum particles is contacted with molten copper. As a result, copper is infiltrated into the voids and interstices between the sintered tungsten or molybdenum particles forming a composite. The disadvantage of the infiltration method is its inability to produce net shape parts. This requires the parts produced by infiltration to be machined into final shape, thereby greatly increasing complexity of manufacture and cost.
In another method which is described in U.S. Pat. No. 3,382,066, a powdery mixture of copper oxide particles and tungsten oxide particles is reduced in a hydrogen atmosphere, the reduced powder is mixed with a binder and the mixture so-obtained compacted and sintered.
In yet another method described in U.S. Pat. No. 5,439,638, a mixture of tungsten powder, copper oxide powder and optionally cobalt powder is milled in an aqueous medium to form a slurry. The liquid is removed from the slurry to form spherical, flowable agglomerates, and the agglomerates are subjected to a reducing atmosphere to form a flowable tungsten/copper composite powder.
A common disadvantage associated with these methods is the necessary reduction of one or more oxides at very high temperatures in hydrogen or other reducing atmospheres. In particular, methods involving the co-reduction of oxide powders involve extra processing steps thereby making them more complex and difficult to control. Accordingly, there is a need for a method of making these composites which is simpler and less expensive.